Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/261

Rh valleys in the neighbourhood, and the general surface-contour of the surrounding district as compared with the country on the western slope of the chain immediately beyond the watershed, where ice is known to have been, and where the hills and dales lose their stern angular character, and become characterized by a soft, rounded, and flowing appearance, indicating unmistakably the operation of divergent forces, and the existence of wholly different conditions, we shall have no difficulty in concluding that glacial or land ice has had no share in their formation or subsequent modification, but that they owe their origin in the first instance to the fracturing of the rocks, and subsequently to the operation of subaerial forces.

Having now pointed out the physical features of the district, I shall proceed to offer some reasons for concluding that during the glacial period these lines of communication were blocked up by snow or ice so as to cut off all connexion between the two sides of this chain of hills. On the approach of the long winter which preceded the period when ice overspread the county of Lancaster and the whole of the northern part of our island, the severity of the climate would gradually increase; and during this time large accumulations of snow would take place, and ice be formed in deep and sheltered situations like those presented by the Walsden, Cliviger, and Todmorden valleys. The snow, thus accumulated to a depth of from 80O to 1000 feet, would, by being partially melted and recongealed, become in time a consolidated compact mass, little if at all inferior to that of ice itself in density and consistency.

Accepting, then, this proposition, we shall have no difficulty in concluding that these bodies, held firmly in their places in the tortuous serrated valleys which are so constructed, and holding such relations to each other that any attempt to move on the part of the accumulations in one of the arms would be resisted and counterbalanced by the opposing force of the other two branches, each of which would have a tendency to move in an opposite direction, would thus be able to offer an effectual resistance to the force of the great northern glacier, on its approach so far south, to dislodge them from their strongly intrenched positions,—the resistance to all motion on their part being still further increased by the presence of the glaciers acting upon the terminal portions of the two arms at the mouths of the valleys by which those bodies, if in motion, would have to emerge, with a force equal to that exerted at the northerly end of the Cliviger gorge, where the glacier would seek to effect an entrance therein, thus completely neutralizing each other, and preventing any motion on their part taking place. The progress of the glacier in its journey south being thus arrested by an impassable barrier, at or near Holmes Chapel, in the Cliviger gorge, where the valley suddenly contracts and becomes hemmed in on both hands by massive beds of grit rocks, in some places almost vertical, it is evident that the ice forcing its way so far would be compelled either to move on over the imbedded and stationary mass, or be deflected from its course, and compelled to take a more westerly direction, part of it finding its way over the pass separating the Easden